Data processing system

ABSTRACT

A data processing system with improved data transfer capabilities. All units in the system, including a random access memory unit, are connected in parallel. Data is transferred between any two units asynchronously with respect to a processor unit which normally controls the system. Other units can obtain system control by making a request which is honored if it has sufficient priority. Transfers requiring processor unit operation are made after an instruction is processed and may divert the processor unit to an interruption routine. Other transfers can be made whenever another unit in the system is not making a transfer. System control is returned to the processor unit or another peripheral unit when the data transfer is completed. If an interruption routine is to be executed, control is returned to the processor directly. Data transfers are controlled by synchronization signals from the controlling peripheral unit and the other unit involved in the transfer.

United States Patent Cohen et al. 14 1 Jan. 9, 1973 s41 DATA PROCESSING SYSTEM 3,430,914 11/1969 Schlaeppi ..340/172.5 CM $332383 51%??? 3523115511113: "133131113? 3mm; 3'' 3,614.140 10/1911 12613 1 et al. ..340/l72.5 3,614,741 10/1971 McFarland et al. ..340/l72.5

Jr., Carlisle, all of Mass.

[73] Assignee: Digital Equipment Corporation, Primary Emmmfl-"paul l Maynard, Mass. Assistant Examiner-Jan E. Rhoads Filed: p 1970 Attorney-Cesart and McKenna [21] Appl. No.: 24,636 [57] ABSTRACT A data processing system with improved data transfer [52] US. Cl ..340/172.5 capabilities. All units in the system. n ding a ran- [51] Int. Cl. ..G06t 3/04,G06f 9/l8 dom access memory unit, are connected in parallel. [58] Field of Search ..340/l72.5 Data is transferred between any two units asynchronously with respect to a processor unit which [56] References Cited normally controls the system. Other units can obtain system control by making a request which is honored UNITED STATES PATENTS if it has sufficient priority. Transfers requiring proces- 3,274,561 9/1966 Hallman =1 al. ..340/172.s SOY unit Operation are made after an instruction is 3,061,192 10/1962 Terzian ....340/l72.5 processed and may divert the processor unit to an in- 3,2l4.739 1 I Gountanis et al- ....340/l72.5 terruption routine. Other transfers can be made when- 3,42i,i50 QUOSIg Bl al............ ever another unit in the ystem is no[ making a i 'i z transfer. System control is returned to the processor 3297994 I967 5 3: y unit or another peripheral unit when the data transfer 3:403:632 10/1968 k'II is completed. If an interruption routine is to be ex- 3 41 39 2 5 Marxhnwwm Mug/1725 ecuted, control is returned to the processor directly. 3,512,136 5/1970 Harmon etal... ....340/172.5 Data transfers are controlled by synchronization 3,370,274 2/1968 Kettley et al.... ....340/172.5 signals from the controlling peripheral unit and the 3,386,082 5/1968 Stafford et al... ....340/l72.5 other unit involved in the transfer, 3,470,542 9/1969 Trantanella ....340/l72.5 3,374,465 3/1968 Richmond et a]. ..340/172.5 27 Claims, 21 Drawing Figures PROCESSOR i J L UNIT 1 L 22K CONTROL CONTROL CONTROL "l" 531". H 599?! PERPt-ERAL P wru 2e /Z6 "5m?" 24 D-DATA A-ADDRESS a;

an BUS neoussr=:

8G BUS WANT -Pn- NON-PROCESSOR REQUEST COMROL J NPG-NON-PROCESSOR arm/r M PROCESSOR INTR INTERRUFT SACK SELECTION ACKNOWLEDGEMENT UNIT BLBY

MSYN MASTER SYNCHRONIZATION 4- PATENTEDJAN 91ers 9.710.324

sum mar 19 /30 t N PROCESSOR UNIT L 22 CONTROL coNTRoL coNTRoL F SECTION SECTION s E 1g PER| PHERAL PERIPHERAL MEMORY UNT N UNIT 1 UNIT 0 DATA q;

A-ADDRESS BR BUS REQUEST g;

as BUS GRANT NPR NoN PRocEssoR REQUEST CONTROL Q NPG NoN PRocEssoR GRANT PROCESSOR SACK SELECTION ACKNOWLEDGEMENT --T |NTR INTERRUPT K BusY c CYCLE coNTRoL Q Q MSYN MASTER SYNCHRONIZATION SSYN SLAVE SYNCHRONIZATION INV E NTORS HAROLD L. MCFARLAND JOHN B COHEN ATTORNEYS PATENTEDJIIII 9 I873 4 MEMORY UNIT SHEET D3 BF 19 5 I EE] CONTROL III 84 SECTION 88 OPERATING PROGRAM INTERRUPTION INSTRUCTIONS ROUTINE INSTRUCTIONS INT ROUTINE l INT ROUTINEE I 86 E 92/ I INT ROUTINEn SUBROUTINE 2 I r90 fiii I fi SUBROUTINE n sP-I FIG. 3

SUBROUTINE SP-n INSTRUCTIONS INVENTORS L. Mc FA RLAND ATTORNEYS PAIENIEDJIIII SIHTa 3.710.324 SHEET DSBF 19 BsR-I TRANSFER THE PC REGISTER CONTENTS TO THE B INPUT CIRCUIT 52 BSR2 TRANSFER THE B INPUT CIRCUIT CONTENTS TO THE BUS ADDRESS REGISTER 34; THEN INCREMENT THE OUTPUT FROM THE ADDER UNIT 46.

UK BSR'3 TRANSFER THE INCREMENTED OUTPUT FROM THE ADDER UNIT 46 TO THE PC REGISTER;

TRANSFER THE INSTRUCTION FROM LOCATION DESIGNATED BY THE BUS ADDRESS REGISTER 34.

DECODE THE INSTRUCTION IN THE I INSTRUCTION DECODER 64.

DOES THE INSTRUCTION DECODE YES AS A "HALT" INSTRUCTION? N0 I MAY THE INSTRUCTION BE EXECUTED YES IMMEDIATELY DOES THE INSTRUCTION HAvE Two NO OPERANO ADDRESSES wITH THE FIRST HAvING A NON-ZERO ADDRESS MODE? YES I USE THE FIRST OPERAND ADDRESS AS A DESIGNATED ADDRESS I USE THE SINGLE OPERAND OR SECOND OPERAND ADDRESS AS A DESIGNATED ADDRESS r BsR-I TRANSFER THE CONTENTS OF THE DESIGNATED REGISTER TO THE B INPUT CIRCUIT 52; FOR MODE -4 OR-S OPERAND ADDRESSES, TRANSFER A DECREMENTING vALUE TO THE A INPUT CIRCUIT4B. BSR-2 TRANSFER THE ADDER UNIT OUTPUT To THE BUS ADDRESS REGISTER 34-, IF ISR THE ADDRESS IS MODE 2 OR -3, 0R TRANSFER AN INCREMENTING vALUE TO DAT, THE A INPUT CIRCUIT 48.

BSR-3 TRANSFER THE ADDER UNIT OUTPUT TO THE SELECTED REGISTER; TRANSFER THE CONTENTS OF THE LOCATION ADDRESSED BY THE BUS ADDRESS REGISTER 34 TO THE B INPUT CIRCUIT 52.

I INVENTORS Q) HAROLD L, MCFARLAND HEN FI G. 6A

ATTORNEYS PAIENIEDJAII 9 I975 SHEET GSUF I9 DoES THE FIRST OPERAND ADDRESS HAvE A MODE -I, YES -2, 0R 4 OPERAND ADDRESS? I NO asR-I IF ADDRESS MODE -6 DR -T, TRANSFER THE B INPUT CIRCUI NO DPERATID ISR aSR-2 TRANSFER THE ADDER UNIT OUTPUT DAT OR To THE BUS ADDRESS REGISTER 34. Dmp BSR'B TRANSFER THE coNTENTS OF THE DESIGNATED REGISTER CONTENTS TO THE A INPUT CIRCUIT 481 ADD INDEX VALUE IN 52- IF OTHER'MODE,

LOCATION ADDRESSED BY THE BUS ADDRESS REGISTER 34 TO THE 8 INPUT CIRCUIT 52 ADDRESS HAVE A MODE '3 DOES THE FIRST OPERAND "5,0R '6 OPERAND ADDRESS YES 15R BSR'S TRANSFER THE coNTENTS DATI 0R OF THE LOCATION ADDRESSED BY THE BUS DATIP ADDRESS REGISTER 34 To THE 9 INPUT BSR'I NO OPERATION. BSR '2 TRANSFER THE ADDER UNIT OUTPUT TO THE BUS ADDRESS REGISTER 34.

CIRCUIT 52 YES NO IS THE OPERAND ADDRESS THE FIRST OF TWO IN THE INSTRUCTION? STORE THE OUTPUT FROM THE ADDER ISR UNIT 46 IN THE SOURCE REGISTER IN THE REGISTER MEMORY 4O (DOES THE SEC ND OPERAN HAVE A MODE -0 OPERAND YES FIG. 6B

INVENTORS HAROLD LI MCFARLAND JOHN B, COHEN PAUL E. JANSON JAMES B. YOUNG JR.

ATTORNEYS PAIENTEDJAII 9 I973 SHEET U7IIF I9 I IS THE INSTRUCTION DECODED AS YES A JMP TRANSFER INSTRUCTION? TRANSFER THE ADDRESS DEFINED BY THE INSTRUCTION OPERAND ADDRESS TO THE PC REGISTER ISR-O IS THE INSTRUCTION DECODED AS A No JSR TRANSFER INSTRUCTION YES I 0 TRANSFER THE ADDRESS DEFINED BY SR- THE INSTRUCTION OPERAND ADDRESS TO THE TEMP REGISTER EXECUTE FIG. 6C

ATTO RN E YS PAIENTEIIJAII 9 m5 ISR- O DATO ISR-I ISR- 3 ISR 4 SHEET UBUF I9 Cvs THE vss BSR-I BSR-2 BSR-3 BSR-O BSR-G BSR- 7 I TRANSrIsER THE PC REGISTER CONTENTS THE 8 INPUT CIRCUIT 52.

TRANSFER THE CONTENTS OF THE ADDER UNIT TO THE R5 REGISTER.

TRANSFER THE CONTENTS OF THE TEMP MEMORY 40 TO THE B REGISTER IN THE REGISTER INPUT CIRCUIT 52.

TRANSFER THE CONTENTS OF THE ADDER THE REGISTER MEMORY 40.

UNIT TO THE PC REGISTER IN INSTRUCTION DECODED AS NO JSR INSTRUCTION A RTS INSTRUCTION IS THE INSTRUCTION DECODED AS NO YES FIG. 7A

INVENTORS HAROLD L. MCFARLAND JOHN B. COHEN PAUL E, JANSON JAMES B. YOUNG JR.

BY m,-

ATTORNEYS PAIENIEDJAII 9mm 3.710.324 SHEET USUF I9 ISR 4 TRANSFER THE R5 REGISTER CONTENTS TO THE 8 INPUT CIRCUIT 52.

TRANSFER THE ADDER UNIT OUTPUT TO lSR-S THE PC REGISTER IN THE REGISTER MEMORY 40 BSR-l TRANSFER THE CONTENTS OF THE SP REGISTER IN THE REGIsTER MEMORY 40 TO THE B INPUT cIRcUIT 52. BSR-2 TRANsFER THE AOOER UNIT OUTPUT To THE BUS AOOREss REGISTER a4,- TRANSFER AN INCREMENTING VALUE TO THE A ISR-6 INPUT CIRCUIT 4e. BSR-3 TRANsFER THE INCREMENTED VALUE FROM THE AOOER UNIT 46 TO THE SP REGISTER IN THE REGISTER MEMORY 40; TRANsFER THE cONTENTs OF THE LOCATION DEFINED BY THE BUS ADDRESS REGIsTER 34 TO THE 8 INPUT CIRCUIT 5g.

TRANsFER THE ADDER UNIT OUTPUT TO THE R5 REGISTER IN THE REGISTER MEMORY 40.

IS THE INSTRUCTION DECODED AS A RTI INSTRUCTION NO YES BSR-I TRANSFER THE CONTENTS OF THE SP REGISTER IN THE REGISTER MEMORY 40 TO THE B INPUT CIRCUIT 52.

BSR-Z TRANSFER THE ADDER UNIT OUTPUT TO THE BUS ADDRESS REGISTER 34',TRANS- |SR 4 FER AN INCREMENTING VALUE TO THE A INPUT CIRCUIT 48.

DATI BSR-3 TRANSFER THE INCREMENTED VALUE FROM THE ADDER UNIT 46 TO THE SP REGISTER IN THE REGISTER MEMORY40,

TRANSFER THE CONTENTS OF THE (:35 LOCATION DEFINED BY THE BUS ADDRESS 65 REGISTER 34 TO B INPUT CIRCUIT 52 INVENTORS HAROLD L. McFARLAND JOHN B. COHEN PAUL E JANSON JAMES B YOUNG JR. BY (7 u 4. 4

ATTORNEYS PAIENIEDJIII 9 I975 ISR-G DATI ISR-T ISR-I ISR-Z SHEET 10 0F 19 TRANSFER THE ADDER UNIT OUTPUT TO THE PC REGISTER IN THE REGISTER MEMORY 40.

BSR-I TRANSFER THE CONTENTS THE SP REG.

ISTER IN THE REGISTER MEMORY 40 TO THE B INPUT CIRCUIT 52.

BSR-Z TRANSFER THE ADDER UNIT OUTPUT TO THE BUS ADDRESS REGISTER 34;

TRANSFER THE ADDER UNIT OUTPUT TO THE STATUS REGISTER 59 IN THE PRIORITY CONTROL UNIT 58.

IS THE INSTRUCTION DECODED AS A )ND BRANCH INSTRUCTION YES I TRANSFER THE CONTENTS OF THE PC REG- ISTER IN THE REGISTER MEMORY 40 TO THE A INPUT CIRCUIT48.

I TRANSFER THE OUTPUT FROM THE ADDER UNIT 46 TO THE PC REGISTER IN THE REGISTER MEMORY 40.

FIG. 7C

INVENTORS HAROLD L. McFARLAND JOHN B COHEN PAUL E. JANSON JAMES B YOUNG JR.

BY (1-1, ,z

ATTORNEYS PATENTEDJAII 9 I973 ISR-4 lSR-4 ISR-4 ISR-4 DATO SHEET llIJF 19 ALTER THE CONDITION CODES IN THE STATUS REGISTER 59 IN THE STATUS UNIT 58.

IS THE INSTRUCTION oecooeo AS A N0 Tsnsn coR CMP INSTRUCTION TRANSFER THE STATUS WORD TO THE MEMORY UNIT 24 FOR STORAGE.

( DOES THE SECOND OR SINGLE PERAND ADDRESS HAVE A MODE- OPERAND ADDRESS YES BSR -6 BSR-T TRANSFER THE DATA FROM THE ADDER UNIT I 46 TO THE REGISTER IN THE REGISTER MEMORII 4O DESIGNATED BY THE OPERAND ADDRESS.

TRANSFER THE DATA FROM THE ADDER UNIT 46 TO THE BUS 30 FOR STORAGE AT THE LOCATION DEFINED BY THE BUS ADDRESS REGISTER CONTENTS WAIT FOR ACKNOWLEDGEMENT THAT THE DATA IS STORED IN THE ADDRESSED LOCATION.

TER M FIG. 7E

INVENTORS HAROLD L. MCFARLAND JOHN B. COHEN PAUL E. JANSON JAMES B. YOUNG JR.

PAIENIEIIJAII 9 I975 ISR -4 DAT I ISR-5 ISR-S DAT I ISR' 7 SHEET 12 0F I9 BSR -I TRANSFER THE TEMP. REGISTER CONTENTS TO THE 8 INPUT CIRCUIT 52.

TRANSFER THE B INPUT CIRCUIT CONTENTS TO THE BUS ADDRESS REGISTER 34; INCREMENT THE B INPUT CIRCUIT CONTENTS BY TRANSFERRING AN INCREMENTING VALUE TO THE A INPUT CIRCUIT 54.

TRANSFER THE ADDER UNIT OUTPUT TO THE TEMP. REGISTER; TRANSFER THE CONTENTS OF THE LOCATION DEFINED BY THE BUS ADDRESS REGISTER 34 TO THE B INPUT CIRCUIT 52.

BSR -3 TRANSFER THE B INPUT CIRCUIT CONTENTS TO THE PC REGISTER.

BSR -2 BSR-3 CIRCUIT 52.

TRANSFER THE INPUT CIRCUIT CONTENTS TO THE STATUS REGISTER 59 IN THE STATUS UNIT 58.

FETCH FIG. 8B

INVENTORS HAROLD L. McFARLAND JOHN B. COHEN PAUL E. JANSON JAMES B. YOUNG JR BY CL:

ATTORNEYS PATENTEUJMI 9 ms SHEET BR? BR6 3 FIG. u BR5 '7 374 HALT 3 DATA J 294 START w 302 CLKBR WATT 3'0 MSYN 06 KET ZYT GRANT & D GRANT NPF E D f- TIMING T 338 UNIT c R I T *3 35 380 340 GRANT L) D SSW CR PROCCNT J 39o 392 1 M/VI s INTR 25s ADRDONE j 254 262 I264 MAP: D MSYN JSR 58 ADRZ 2 0 DATI M J DATIP 252 INVENTORS esRz HAROLD MCFARLAND JOHN B. COHEN BsRT PAUL E. JANSON BYJAMES a. YOUNG JR.

DATA CLEAR A A ATTORNEYS PAIENIEIIJAII 9 I973 ISR-D ISR-I ISR-Z ISR-3 SIIEEI 1 IIIFI9 TRANSFER THE CONTENTS OF THE LOCATION DEFINED BY THE OPERAND ADDRESS FROM THE SELECTED REG ISTER IN THE REGISTER MEMORY 40'IO ONE OF THE INPUT CIRCUITS 48 OR 52.

DOES THE INSTRUCTION HAVE TWO OPERAND ADDRESSES )YES TRANSFER THE CONTENTS OF THE SOURCE REGISTER IN THE REGISTER MEMORY 4OTO THE OTHER LATCH.

DOES THE INSTRUCTION REQUIRE THE )NO ADDITION OF CONSTANTS YES TRANSFER THE CONSTANT TO THE APPRO- PRIATE ONE OF INPUT CIRCUITS 48 OR 52.

I IS THE INSTRUCTION DECODED AS A BIT OR A BIC INSTRUCTION YES TRANSFER THE CONTENTS OF THEIADDER UNIT 46 TO THE TEMP REGISTER IN THE REGISTER MEMORY 40.

TRANSFER THE TEMP REGISTER CONTENTS IN THE REGISTER MEMORY 40 TO THE A INPUT CIRCUIT 48.

FIG. 70

INVENTORS HAROLD LI MCFARLAND JOHN B. COHEN PAUL E JANSON JAMES B. YOUNG JR./ BY f/ ATTORNEYS PAIENIEDJAII QISIS 3.710.324

SHEET lSIIF 19 TERM DO ANY BUS REQUEST SIGNALS FROM )NO PRIORITY CONTROL UNIT 62 EXIST YES I PROCESSOR UNIT 22 RELINOUISHES CONTROL OF BUS so DEPENDING UPON PRIORITY REQUESTING PERIPHERAL TRANSMITS AN |SR ADDRESS TO THE TEMP REGISTER IN THE REGISTER MEMORY 4o.

BSR-I TRANSFER THE SP REGISTER CONTENTS TO THE B INPUT CIRCUIT 52 AND A DECRE- MENTING QUANTITY TO A INPUT CIRCUIT48.

BSR-2 TRANSFER THE ADDER UNIT OUTPUT TO THE BUS ADDRESS REGISTER 34.

BSR-3 TRANSFER THE ADDER UNIT OUTPUT TO ISR- 2 THE SP REGISTER. BSR-4 NO OPERATION. DATO BSR-G TRANSFER THE STATUS REGISTER CON TENTS FROM THE STATUS UNIT 50 TO THE BUS 3O BSR-7 WAIT FOR ACKNOWLEDGEMENT THAT THE STATUS WORD IS STORED IN THE MEMORY UNIT 24 AT THE LOCATION DEFINED BY THE BUS ADDRESS REGISTER 34.

ISR 3 BSR-0 TRANSFER PC REGISTER CONTENTS TO THE B INPUT CIRCUIT 52. DATO BSR -G TRANSFER THE B INPUT CIRCUIT CONTENTS TO THE BUS 30.

BSR WAIT FOR ACKNOWLEDGEMENT THAT THE PROGRAM COUNT IS STORED IN THE MEMORY UNIT 24 AT THE LOCATION DEFINED BY THE BUS ADDRESS REGISTER 34.

FIG. 8A HAROLD E I'IZTSI R EZSD JOHN B COHEN PAUL E JANSON JAMES B. YOUNG JR.

AT TORNE YS PATENTEUJAII 9I975 3.710.324

SHEET 180F 19 CLK IIWILIIIIIIIL SCLK m READ/WRITE CYCLES \D\I,ZI3QIl'2361l213lQ WRITE l I I SHIFT REGISTER 4 I .2 3-|+ STATE J --ISR-fi TIMING uNIT es INSTRUCTION I76 SCLK SHIFTREGISTER I TIMING SIGNAL I TIMING CLOCK GENERATOR i CIRCUIT (01.x) I'+ U FIG.9B CLE KR CONTROL UNIT 60 -BSR'9 -T BSR'| BUS SHIFT I REGSTER HAROLD L M'QXIEI'QSS C SIGNAL GENERATOR I JOHN H COHEN I PAUL E. JANSON QBSR-Y JAMES B. YOUNG JR. 2 BY ATTORNEYS 

1. A data processing system including a processor unit normally controlling the system for processing information including data and instructions and a plurality of other units each having means for transmitting or receiving information, said other units including a random access memory unit for storing information and at least one peripheral unit including means for generating a system control request signal when it is ready to transfer information, said system comprising: A. a bus for connecting said processor unit and each of said other units in parallel, said processor and peripheral units each having a relative priority in the system, B. priority means responsive to a system control request signal on said bus for selecting a requesting peripheral unit according to its priority and for enabling said selected peripheral unit to couple signals onto said bus, C. means in each peripheral unit for indicating an interval during which the peripheral unit can transfer data, each indicating means being enabled when its corresponding peripheral unit is selected by said priority means, D. means in each peripheral unit responsive to said indicating means for generating a busy signal onto said bus for transmission to said priority means and all peripheral units connected to said bus, said means in the selected peripheral unit generating the busy signal upon assuming control of said bus thereby indicating that the selected peripheral unit controls said bus, E. means in each peripheral unit responsive to said indicating means for disabling said busy signal generating means at the end of the interval, each disabling means being operable when its corresponding peripheral unit is selected by said priority means, and F. means in each peripheral unit for coupling signals onto said bus and to identify another unit in the system to thereby enable the selected peripheral unit to transfer information to or from that other unit, each coupling means being operable when its corresponding peripheral unit is selected by said priority means.
 2. A data processing system as recited in claim 1 wherein said bus includes control, address and data signal paths, said control and address signal paths being connected to each unit in said system, said system additionally comprising means in each unit responsive to signals on said address and control signal paths for selectively enabling itself to couple signals onto or from said data signal path.
 2. means for generating control signals for coupling said bus data signal path to said addressed unit to effect the information transfer,
 2. means for generating control signals onto said control signal path including a delayed master synchronization signal, and
 2. means for generating control signals onto said control signal path including a delayed master synchronization signal, and
 2. means for generating control signals onto said control signal path including a delayed master synchronization signal, and B. said second unit comprising means responsive to said master synchronization signal for generating a slave synchronization signal and transferring information signals onto said data path, and C. said first unit additionally comprising means responsive to said slave synchronization signal for inhibiting the address and control signals, said second unit thereafter deactivating said information and slave synchronization signals.
 2. means for generating control signals onto said control signal paths including a delayed master synchronization signal, and B. said second unit comprising means responsive to said master synchronization signal for generating a slave synchronization signal and transferring information signals onto said data path, and C. said first unit additionally comprising means responsive to said slave synchronization signal for inhibiting the address and control signals, said second unit thereafter deactivating said information and slave synchronization signals.
 3. means for transferring information signals onto the data signal path, B. said second unit comprising means responsive to the master synchronization signal for generating a slave synchronization signal and transferring information signals into said second unit from said data path, and C. said first unit comprising means responsive to said slave synchronization signal for inhibiting the address control and information signals, said second until thereafter deactivating said slave synchronization signal.
 3. means for transferring information signals onto the data signal path, B. said second unit comprising means responsive to said master synchronization signal for generating a slave synchronization signal and transferring informaTion signals into said second unit from said data path, and C. said first unit additionally comprising means responsive to said slave synchronization signal for inhibiting the address, control and information signals, said second unit thereafter deactivating said slave synchronization signal.
 3. said terminating means terminating the busy signal when said peripheral unit completes an information word transfer, and B. means in said processor unit responsive to a busy signal termination for causing said processor unit to assert a busy signal.
 3. A data processing system as recited in claim 2 wherein: A. said priority means is responsive to the availability of said bus for a transfer and the priority of the request signal for thereafter selecting a peripheral unit in response to a request signal and the relative peripheral priority, and B. said indicating means includes means responsive to a busy signal termination on said bus for enabling said selected peripheraL unit to assume system control.
 4. A data processing system as recited in claim 3 wherein said processor unit can have one of a plurality of priorities, said priority means additionally comprising: A. means for storing the current operating priority of the system, and B. a comparison unit for comparing the request signal priority with the current operating priority and for generating a selection signal when the request priority exceeds the current operating priority.
 5. A data processing system as recited in claim 4 wherein each peripheral unit additionally comprises: A. means responsive to the selection signal from said priority means for selecting itself when it has generated a system control request signal, B. means responsive to the coincidence of the selection signal and the request signal for transmitting an acknowledgement signal to said priority means, and C. said indicating means being responsive to the coincidence of the request signal and selection signal for selecting another unit to initiate a transfer of information to or from said selected peripheral unit.
 6. A data processing system as recited in claim 5 wherein: A. said priority means includes means for disabling itself in response to the acknowledgement signal, and B. said processor unit is responsive to the acknowledgement signal and to the completion of a preceding transfer for terminating its busy signal and thereby enabling the selected peripheral unit to assume system control.
 7. A data processing system as recited in claim 6 wherein at least one of said peripheral units is adapted for transferring an information word independently of said processor unit after given information transfers to or from said processor unit, each independently operable peripheral unit comprising: A. means for generating a first request signal having the highest system priority to said priority unit, B. said priority means being responsive to the first request signal and a given transfer over said bus for transferring system control to said independently operable peripheral unit on the completion of the given transfer to enable said independently operable peripheral unit to transfer the information.
 8. A data processing system as recited in claim 7 wherein: A. said independently operable peripheral unit comprises:
 9. A data processing system as recited in claim 6 wherein: A. at least one of said peripheral units is adapted to generate a second request signal having a predetermined priority level, and B. said priority unit includes means responsive an information transfer for an instruction executed by said processor unit for selecting a peripheral unit for control when it has made a control request, said selected peripheral unit assuming control after the instruction is executed by said processor unit.
 10. A data processing system as recited in claim 9 wherein: A. each peripheral unit includes means for energizing said address and control paths and means responsive to signals on said control and address signal paths for transferring data, said selected peripheral unit asserting its busy signal upon assuming system control and terminating the busy signal after the data transfer is finished, and B. said processor unit includes means responsive to the termination of the busy signal from said selected peripheral unit for enabling another peripheral unit or said processor unit to assume system control.
 11. A data processing system as recited in claim 9 wherein each peripheral unit includes: A. means for energizing said address, control and data paths, and B. means responsive to peripheral unit conditions requiring an interruption routine for generating an interrupting signal onto said control signal path and a memory unit address onto said data path for transfer to said processor unit to interrupt processor unit operations.
 12. A data processing system as recited in claim 11 additionally comprising: A. means in said processor unit responsive to the interruption signal and the memory address on said control and data signal paths, respectively, for transmitting an acknowledgement signal to said peripheral units when said processor unit finishes processing its current instruction, and B. means in each peripheral unit responding to the acknowledgement signal by terminating the busy signal, when generated, and enabling the processor unit to obtain immediate system control.
 13. A data processing system as recited in claim 9 wherein each of the second request signals has one of a plurality of priorities, a given request signal identifying a group of peripheral units having the same given priority, said data processing systems additionally comprising: A. means in said priority unit for generating a selection signal for each group of peripheral units with the same priority level, a control path being energized by the selection signals, B. means in each peripheral unit connected for serially coupling the selection signal through all peripheral units in its group adapted to make requests at the associated priority level, and C. means in each peripheral unit responsive to coincidence of request and selection signals for inhibiting the selection signal whereby each peripheral unit having a given priority level is further arranged into sub-priorities by its relative series position with respect to said priority unit.
 14. A data processing system as recited in claim 6 additionally comprising: A. means in each peripheral unit responsive to said indicating means and said processor unit for generating a master synchronization signal to effect an information transfer over said bus, and B. means in each unit responsive to a master synchronization signal and selection for transmitting a slave synchronization signal to acknowledge the data transfer, said terminating means being responsive to said slave synchronization signal.
 15. A data processing system as recited in claim 6 wherein information is transferred as signals under the control of a first unit in said system from a second unit, A. said first unit comprising:
 16. A data processing system as recited in claim 6 wherein information is transferred as signals under the control of a first unit in said system to a second unit, A. said first unit comprising:
 17. A data handling system including a plurality of units, each having means for transmitting or receiving information, at least one of said units being a peripheral unit including means for generating a system control request signal when it is ready to transfer information, said system comprising: A. a bus for connecting each of said units in parallel, each unit having a relative priority in the system, B. priority means responsive to a system control request signal on said bus for selecting a requesting peripheral unit according to its priority and for enabling said selected peripheral unit to couple signals onto said bus, C. means in each peripheral unit for indicating an interval during which the peripheral unit can transfer data, each indicating means being enabled when its corresponding peripheral unit is selected by said priority means, D. means in each peripheral unit responsive to said indicating means for generating a busy signal onto said bus for transmission to said priority means and all peripheral units connected to said bus, said means in a selected peripheral unit generating the busy signal upon assuming control of the bus thereby indicating that the selected peripheral unit controls said bus, E. means in each peripheral unit responsive to said indicating means for disabling said busy signal generating means at the end of the interval, each disabling means being operable when its corresponding peripheral unit is selected by said priority means, and F. means in each peripheral unit for coupling signals onto said bus to identify another unit in the system to thereby enable the selected peripheral unit to transfer information to or from that other unit, each coupling means being operable when its corresponding peripheral unit is selected by said priority means.
 18. A data handling system as recited in claim 17 wherein said bus includes control, address and data signal paths, said control and address signal paths being connected to each unit in said system, said system additionally comprising means in each unit responsive to signals on said addressing and control signal paths for selectively enabling itself to couple signals onto or from said data signal path.
 19. A data handling system as recited in claim 18 wherein: A. said priority means is responsive to the availability of said bus for a transfer and the priority of the request signal for thereafter selecting a peripheral unit in response to a request signal and the relative peripheral priority, and B. said indicating means includes means responsive to a busy signal termination on said bus for enabling said selected peripheral unit to assume system control.
 20. A data handling system as recited in claim 19 wherein each peripheral unit additionally comprises: A. means responsive to the selection signal from said priority means for selecting itself when it has generated a system control request signal, B. means responsive to the coincidence of the selection signal and the request signal for transmitting an acknowledgement signal to said priority means, and C. said indicating means being responsive to the coincidence of the request signal and selection signal for selecting another unit to initiate a transfer of information to or from said selected peripheral unit.
 21. A data handling system as recited in claim 20 wherein: A. said priority means includes means for disabling itself in response to the acknowledgement signal, and B. each of said peripheral units includes means responsive to the acknowledgement signal and to the completion of a preceding data transfer for terminating its busy signal and thereby enabliNg the selected peripheral unit to assume system control.
 22. A data handling system as recited in claim 21 wherein: A. each of said peripheral units comprises means for generating a request signal, and B. said priority means is responsive to the request signal and the absence of data on said bus for transferring system control to a peripheral unit which has generated a request signal to enable said peripheral unit to transfer information.
 23. A data handling system as recited in claim 22 wherein each peripheral unit comprises: A. means for addressing one of said other units in said system, and B. means for generating control signals for coupling said bus data path signal path to said addressed unit to effect the information transfer, C. said terminating means terminating the busy signal when said indicating means completes an information word transfer interval.
 24. A data handling system as recited in claim 23 wherein at least two peripheral units, arranged in a predetermined priority with respect to each other, generate their respective request signals onto the same control path, said data handling system additionally comprising: A. means in said priority unit for generating a selection signal onto another control path, B. means in each peripheral unit connected for coupling the selection signal through successive peripheral units in the order of their priority, and C. means in each peripheral unit responsive to the coincidence of request and selection signals for inhibiting the selection signal whereby each peripheral unit is selected in its priority.
 25. A data handling system as recited in claim 21 additionally comprising: A. means in each peripheral unit responsive to said indicating means for generating a master synchronization signal to effect an information transfer over said bus, and B. means in each unit responsive to a master synchronization signal and its selection for transmitting a slave synchronization signal to acknowledge the data transfer, said terminating means being responsive to said slave synchronization signal.
 26. A data handling system as recited in claim 21 wherein information is transferred as signals under the control of a first peripheral unit in said system from a second unit, A. said first unit comprising:
 27. A data handling system as recited in claim 21 wherein information is transferred as signals under the control of a first peripheral unit in said system to a second unit, A. said first unit comprising: 